This invention relates to a method of kneading rubber.
In the tire industry, heretofore rubber blocks only, or rubber blocks together with chemicals such as sulfur and carbon are kneaded in a kneading mixer called "Banbury mixer" so that the degree of plasticity is lowered.
The kneading mixer of this type is so slow in kneading speed that it is necessary to continue the kneading operation for a long period of time. However, such a long kneading operation would increase the temperature of the rubber thereby to cause a vulcanization reaction to adversely affect the quality of the rubber.
For the purpose of eliminating this difficulty, heretofore the following method is employed: When the temperature of the rubber is increased to a predetermined temperature which is lower than the quality change start temperature, the rubber is taken out of the kneading mixer and cooled down. Then, the rubber thus cooled is kneaded in the kneading mixer again until the degree of plasticity of the rubber reaches a predetermined value. Therefore, the conventional method is disadvantageous in that the productivity is low, and the consumption of energy is large. In the conventional method, while being drawn out of the kneading mixer the kneaded rubber is formed into a rubber sheet about 8 mm in thickness, however, in the case of such a heavy rubber sheet, the rubber is not kneaded at all.